There is known a waveguide bend that connects two waveguides which differ in waveguide axis direction. The conventional waveguide bend connects waveguides so that respective electric field planes (E-planes) or magnetic field planes (H-planes) of the two waveguides that are connected is in parallel with each other.
There is known a post wall waveguide (also called a dielectric waveguide or a substrate integrated waveguide and the like) that is constituted of a via-hole array that is formed on a dielectric substrate, and copper foils bonded onto both surfaces of the dielectric substrate. As a coupler that connects a post wall waveguide and a waveguide, there is a coupler that uses a bend structure.
In the conventional waveguide bend structure described above, the E-planes or the H-planes of the two waveguides that differ in waveguide axis direction are disposed to be parallel with each other. However, the disposition is sometimes required so that the H-planes of one of the waveguides and the E-planes of the other one of the waveguides is in parallel. If both are coupled so that the H-planes of one of the waveguides and the E-planes of the other one of the waveguides are parallel with each other, signals cannot be coupled between these waveguides. For example, when a high-frequency signal of a TE10 mode is inputted from one of the waveguides, the high-frequency signal is brought into a TM mode having an electric field component in the waveguide axis direction, with respect to the other one of the waveguides. Therefore, the high-frequency signal has a higher-order mode with respect to the other one of the waveguides to be cut off and cannot be coupled.